Researchers at the University of Maryland and the USDA uncovered several links in the chain of factors contributing to massive honeybee losses seen around the country.

Beekeepers have been reporting entire hive losses since 2006, when the media dubbed the phenomenon Colony Collapse Disorder (CCD). Several studies have pointed to poor nutrition, pesticide, pests, and pathogens; however, no single smoking gun has emerged.

“Increasingly we’re thinking it’s a combination of factors coming together and setting colonies up for decline,” said Dennis vanEnglesdorp, an entomology professor at the University of Maryland. “So we wanted to look at what pesticides honeybees are exposed to and what affect those pesticides have on their ability to fight infection of the fungal disease Nosema.”

VanEnglesdorp teamed up with Jeffrey Pettis at the USDA to collect and analyze pollen from fields between Delaware and Maine. Their research team took samples from nine commercial honeybee colonies for each of seven different crops. The team then analyzed the samples for agricultural chemicals, including insecticides and fungicides applied to crops by farmers and miticides applied to hives by beekeepers.

The samples contained an average of nine different pesticides; one sample contained as many as 21 different chemicals. All of the chemicals occurred at what is considered sub-lethal dosage. However, when researchers fed those samples to healthy bees, they became three times as likely to contract Nosema as healthy bees that did not eat contaminated pollen.

The results suggest that even at sub-lethal doses, the affects of agricultural chemicals can compromise bees’ biological defenses to the fungal parasite. These findings add further merit to the general theory that a series of factors are working together to cause the massive bee die offs.

“It’s not that pesticides are the problem. It’s not that Nosema is the problem…Nosema itself isn’t that big of a deal. However, it becomes a health problem once the bees have been exposed to all these pesticides,” said Cory Stanley Stahr, a post-doctoral researcher at the University of Florida and bee specialist who was not involved in the study.

Stanley-Stahr said that the study also helped confirm some long held suspicions of bee specialists about the affects of synthetic chemicals on honeybees.

“It’s generally thought in agriculture that fungicides do not affect bees. Bee scientists have been suspicious of this for some time now. This study gives hard evidence to be able to take to industry and to growers and show them that fungicides are a concern for bees.”

VanEnglesdorp hopes that this research will inform labeling requirements for fungicides. “Insecticides have language on their label that says don’t spray on flowering plants where bees are foraging. There is no such warning for fungicide. This suggests that we should reconsider that labeling,” he said.

However, farmers are not responsible for all of the chemicals. Beekeepers frequently struggle with the varroa mite, a common pest plaguing honeybees. Miticides are designed to kill these mites. However, trying to kill an insect on an insect can be a delicate balancing act. “It’s not a surprise that the miticides are affecting the bees because there’s been a lot of research in recent years that shows this, which is why a lot of beekeepers have been making a big move to “softer miticides” or non-chemical means of mite control,” Stanley-Stahr said.

What was surprising were the types of miticides that showed up in the pollen samples, vanEnglesdorp said. “Some of the miticides that we found we know haven’t been applied for years. We know that the chemicals get trapped in the wax but we don’t know how these residues from years past are getting out into the pollen traps,” he said.

“This is kind of concerning because if there is a way for a miticide that is inside of the hive to somehow get into the environment and be brought back into a hive, that implies that the choices of one beekeeper affect another beekeepers bees,” Stanley-Stahr said.

Stanley-Stahr adds that these same chemicals could be taking just as big, if not bigger, toll on the country’s 4,000 native species of bees. (The honeybee originally hails from Europe.) “We can’t even begin to fathom what the bigger picture is and what the impact is on the other 400 species of bees in this country.”